Taking your choice of machine first, here are some things you need to think about.
Forget a massive machine with huge power. A small- to mid-capacity bike will be much more economical, have all the urge you need to make progress, be light, slim and easy to drive through traffic (and to turn and park), and should have a nice, smooth power delivery to make tight urban riding a cinch.
You want an upright riding position, which will allow you a clear view ahead and peripherally, make it easy to turn your head, and should give you the best view via the mirrors. Until you take a bike for test ride you won’t know whether the mirrors are brilliant or useless. And what suits one rider may not suit another. If the mirrors are blurred by vibration or only give a good view of your elbows, avoid.
Ideally you want a bike with light, smooth clutch and throttle action. ABS is a big plus. Judging grip on well-used city streets is tough.
Adjustable peg and seat height is great. As is a comfy seat with a relaxed reach to the pegs so you don’t have to fold your knees up.
A centre stand is a real boon. You’ll be doing a lot of miles in all weathers so your chain will need cleaning, lubing and adjusting regularly. Unless, that is, you choose a belt or shaft drive. Neither requires the frequent attention of a chain.
If your commute is strictly urban, there’s a good case for choosing a scooter. There are, however, a lot of cheap and sometimes nasty items out there. Best go with something from the big Japanese manufacturers or Italy’s Piaggio group. There’s a good reason scooters are popular for commuting, as they offer protection for a lot of your body. So a fairing is good.
If you do a lot of distance out of town consider a maxi-scooter like Suzuki’s Burgman, Yamaha’s T-Max, BMW’s C600/650 range or similar. There are plenty of great mid-capacity motorcycles to choose from. Suzuki’s faired GSX650F and Yamaha’s FZ6-R, for example, are ideal all rounders that meet the above criteria (though they’re chain drive). Ditto, Kawasaki’s 250, 300 and 650 Ninjas. Honda’s CB500 range comes in adventure, sports and naked guises, plus there’s the hugely economical NC700S and X. If you are prepared to sacrifice weather protection for great fuel economy and a lot of fun, try KTM’s smaller (125, 200 or 390) Duke range. Small capacity trail bikes are another option, offered by most major manufacturers, but they too lack weather protection.